This invention relates generally to pressure responsive devices and more particularly to one shot hermetically sealed pressure relief valves.
There has been a need for a pressure relief valve which can be very accurately calibrated. Prior art pressure relief valves involved the use of a valve member, a valve seat and a biasing means for holding the valve member in engagement with the valve seat. These relief valves have been acceptable for certain applications but lack the reliability and accuracy needed for certain precise applications such as in coolant systems for computers. Additionally, typical prior art relief valves are not hermetically sealed to provide high reliability and accuracy in all environments.
Accordingly it is an object of the present invention to provide an improved pressure relief valve.
It is another object of this invention to provide a pressure relief valve which can be hermetically sealed.
It is still another object of this invention to provide a pressure relief valve which is extremely accurate and reliable in operation.
It is yet another object of this invention to provide a pressure relief valve which is a one-shot device which can be easily calibrated.
It is still a further object of this invention to provide a pressure relief valve of simple construction which can be easily assembled. Other objects and features will be in part apparent and in part pointed out hereinafter.
Briefly, the pressure relief valve of this invention comprises a housing member with a port fitting which at one end connects to a pressure zone and at the other end leads into a central cavity or chamber within the housing. The central chamber is sealingly divided into a first or top portion and a second or bottom portion by a thin membrane fixedly secured within the housing around its perimeter. A snap-acting disc member with a central aperture therein is fixedly secured adjacent the membrane in the bottom portion of the chamber on the opposite side of the thin membrane from the port fitting. Secured in the bottom of the housing is a hollow piercing member which extends up into the bottom portion of the chamber in axial registry with the center aperture of the snap-acting disc.
The snap-acting disc member is calibrated to snap over center at a predetermined over pressure condition and is initially positioned in a concave upward position relative to the piercing member. Upon the occurrence of the over pressure condition, the disc snaps to an inverted dish-shaped configuration causing the piercing member to extend up through the central aperture in the disc. Due to the pressure on the membrane member, the membrane follows the disc, piercing itself on the piercing member to cause venting of the over pressure condition through the hollow piercing member.